Consul vs etcd: What are the differences?

Consul and etcd are both key-value stores that are used for service discovery and distributed configuration management. Here are the key differences between them.

1. Data Consistency Mechanism: Consul uses a strong consistency mechanism to ensure that all nodes in the cluster have the same view of the key-value store. This is achieved through the use of a distributed consensus algorithm based on Raft protocol. In contrast, etcd uses a weaker consistency mechanism where eventual consistency is achieved through gossip-based protocol.

2. Service Discovery Features: Consul provides rich service discovery features such as service registration, health checks, and DNS-based service discovery. It also supports service segmentation and advanced service routing capabilities. On the other hand, etcd focuses more on providing a simple and reliable distributed key-value store and does not have the same level of built-in service discovery features as Consul.

3. Cross-Datacenter Replication: Consul has built-in support for cross-datacenter replication, allowing the key-value data to be synchronized across multiple datacenters. This feature enables the creation of globally distributed systems with Consul. In contrast, etcd does not have built-in support for cross-datacenter replication, although it can be achieved through custom implementations.

4. Monitoring and Metrics: Consul provides a comprehensive set of monitoring and metrics capabilities, allowing users to monitor the health and performance of their Consul cluster. It also has built-in support for integrating with popular monitoring tools such as Prometheus. On the other hand, etcd does not have the same level of built-in monitoring and metrics capabilities as Consul.

5. Consul Connect: Consul has a feature called Consul Connect, which provides a secure service-to-service communication framework. It allows services in Consul to communicate with each other securely, even across different datacenters. ETCD does not have a similar built-in feature for secure service-to-service communication.

6. Ease of Deployment and Configuration: Consul is designed to be easy to deploy and configure, with a single binary release that includes all the necessary components. It also provides a web-based UI for managing and monitoring the Consul cluster. On the other hand, etcd requires more manual configuration and setup, and does not have a web-based UI for managing the etcd cluster.

In summary, Consul is known for its additional features like service health monitoring and multi-datacenter support, making it suitable for complex network architectures. Etcd, an open-source project primarily used by Kubernetes, focuses on simplicity and consistency, providing a reliable key-value store for distributed systems.